The present invention generally relates to an ink jet record apparatus, and more particularly to an ink jet record apparatus for driving and operating a drop-on-demand type ink jet head using a piezoelectric element, which may be applied to an ink jet printer and the like.
Conventionally, there are several non-impact type printers, especially an ink jet printer using a ink jet head with a piezoelectric element, or a bubble jet printer using a heating element. Recently, there has been a demand in the field for such conventional recording apparatus having a high-quality half tone recording capability. To achieve a desired half tone recording by means of the conventional recording apparatus, there are two methods that have been used primarily by the conventional recording apparatus. One method is to vary a pulse width of a drive signal to be applied to a ink jet head of the recording apparatus for controlling the size of ink dots on paper, and the other is to vary a voltage of a drive signal applied to the ink jet head. The ink jet printer usually employs either of the two methods described above. However, in the case where the former method is used, the pulse width can be varied through a digital signal processing, but it is difficult to change significantly the diameter of an ink drop come out from a nozzle of the ink jet head. Also, in the case where the latter method is used, it is necessary to use an analog signal processing to vary a drive voltage applied to the ink jet head, which requires a complicated drive circuit in the recording apparatus, causing the manufacturing cost to be high.
In addition, there is another method that has been used by the conventional recording apparatus. In this method, the weight of an ink droplet come out from the nozzle of the ink jet head is varied to control the size of the ink dots on the paper. To change the weight of the ink droplet, it is necessary to adjust a drive voltage applied to the ink jet head. It is known that the ink drop weight is varied in proportion to a change in the drive voltage applied to the ink jet head, and that the ink jet speed is also changed in proportion to a change in the drive voltage applied to the ink jet head. If the ink droplet weight is changed to be smaller than the current ink droplet weight, the drive voltage must be varied in accordance with the change in the ink droplet weight, and thereby the ink jet speed becomes smaller. For instance, in a serial scan type ink jet recording apparatus, the ink jet head is moved in a main scan direction while ink comes out from the nozzle of the ink jet head, and therefore variations of the ink jet speed may influence significantly the accuracy with which ink dots are positioned on paper. When the speed of movement of the ink jet head in the main scan direction is assumed to be constant, it is desired that the ink jet speed be set to a relatively large value more accurate position ink dots on paper, because the ink jet speed set to a relatively large value can be adjusted within a wide range of allowable variations. However, in a case where the above conventional method is applicable for practical use, there is a problem in that the range of allowable variations in ink jet speed is limited. Also, determining an appropriate ink jet speed for the ink jet head is quite difficult when the ink droplet weight is made very small, as the ink jet speed is determined based on a change in the ink droplet weight, and when the ink droplet weight is small, the ink jet speed lies in a narrow range of allowable variations.